Biosolids or sludges are the solid component of treated wastewater commonly produced by municipalities and industry. Dried biosolid-containing materials are increasingly being produced as a means of converting municipal biosolids or sludges into materials which may beneficially be used for soil conditioning or agricultural fertilizers. These materials are usually formed into granules, pellets, grains, particles, extrusions or other forms with dryness exceeding 80%, and more often, exceeding 95%. When these materials are statically stored in dry ambient conditions, especially in large bulk quantities, cooling that would counter the chemical self-heating can be prevented by the thermal insulation properties of the stored material. Consequently, these materials can slowly chemically self-heat to temperatures commonly exceeding 400° F. (204° C.).
The term organically-enhanced inorganic fertilizer refers to any inorganic fertilizer that is combined with organic materials, such as biosolids, to form a fertilizer. The organic materials can be combined with the inorganic materials prior to, during or after the formation of the inorganic fertilizer.
Chemical self-heating occurs commonly in stored dried biosolids pellets as processed from many municipalities wastewater biosolids or sludges. A material that has experienced some chemical self heating upon long term storage, but significantly less than experienced by dried biosolids that do not contain any major inorganic component, is an organically-enhanced inorganic fertilizer that is described in U.S. Pat. Nos. 5,984,992 and 6,159,263. These patents describe an organically enhanced inorganic fertilizer made by reacting concentrated sulfuric acid with anhydrous ammonia, while adding fluidized municipal biosolids, ostensibly as an agent to cool the reaction of the concentrated acid and base. The material is then granulated, dried, sized and treated with various hardening and de-dusting agents. The resulting product is a dried (98-99.5% solids) granular material that is agriculturally valuable as an ammonium sulfate fertilizer and also contains organic compounds contributed by the biosolids.